A technique described in Patent Literature 1 has been known as a conventional technique of a belt-type continuously variable transmission in which a driving force is transmitted with a belt being wound across a pair of pulleys having a variable groove width.
In the belt-type continuously variable transmission described in Patent Literature 1, a movable sheave is provided with a hydraulic cylinder. The belt-type continuously variable transmission electrically controls an operation of the hydraulic cylinder for changing the groove width (the position of the movable sheave) of the pulley on the basis of signals from various sensors such as a vehicle speed sensor and an accelerator pedal position sensor so that the transmission ratio in the belt-type continuously variable transmission is changed as desired.
The belt-type continuously variable transmission described in Patent Literature 1 has a disadvantage that a complicated configuration is required for electrically controlling the hydraulic cylinder. Accordingly, there exists a technique for controlling the operation of the hydraulic cylinder while detecting (feedback) the slid position of the movable sheave by using a mechanical hydraulic servo mechanism including a servo spool, a feedback spool, etc.
However, with such a conventional technique, when the pressure in the hydraulic cylinder drops because a driving source such as an engine stops or due to other reasons, the movable sheave might slide by the tensile force of the belt, and the servo spool might slide along with the sliding of the movable sheave. That is to say, when the driving source stops, the servo spool might slide against an operator's will. Accordingly, it is disadvantageous because the operator might have a sense of incongruity.